Toothed Wheel Ribbed Rim Casting and Overmolding
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Solution Overview
Problem
Current methods for manufacturing toothed wheels, such as overmolding, lead to polymer chain severing due to shear and self-heating, resulting in suboptimal mechanical resistance, material overconsumption, and challenges in achieving a strong junction between the hub and rim, while also increasing the wheel's weight.
Innovation Solution
A method involving a tubular preform manufacturing step by casting a polymerizable liquid in a mold, followed by cutting to form a rim, and an overmolding step with a central support member to create an intermediate disc for attachment, ensuring polymer chains are not damaged and allowing for robust, lightweight wheel production with improved torsional resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If overmolding operation is used to manufacture toothed wheels, then the rim can be produced around a hub insert, but the polymer material is subjected to shear and self-heating effects causing polymer chain severing and reduced mechanical resistance
Solution Approach 1:
The invention changes the processing parameters by using a two-stage process: first casting the rim at low temperature to preserve polymer chain integrity, then selectively heating only the attachment reliefs in a second step to enable proper bonding. This resolves the contradiction by avoiding the shear and self-heating effects of conventional overmolding while still achieving the necessary junction strength.
Solution Approach 2:
The manufacturing process is segmented into distinct stages: casting the rim separately, then performing a second operation to create attachment reliefs. This segmentation allows the rim material to be formed without damaging shear forces, while the attachment features are created subsequently under controlled conditions, thereby preserving polymer chain integrity while ensuring proper hub junction.
2Strength
If sprues with considerable volume are used to limit shear effects during overmolding, then polymer chain damage is reduced, but raw material and energy consumption increases
Solution Approach 1:
The invention extracts and eliminates the need for large-volume sprues by using a casting process that directly forms the rim around the hub insert without requiring extensive material flow paths. The rim material is deposited precisely where needed, removing the wasteful sprue system entirely and thereby preserving polymer chain integrity without increasing material consumption.
Solution Approach 2:
The casting process is designed to be self-sufficient, requiring no additional sprues or gating systems to deliver material to the mold cavity. The rim material is cast directly into position, making the process inherently efficient without the material overhead of conventional injection molding sprues, thus avoiding both polymer damage and material waste.
3Strength
If complex attachment reliefs are created on the hub insert to ensure satisfactory junction, then torsional shear resistance is improved, but the manufacture of the insert becomes complicated
Solution Approach 1:
Instead of creating complex attachment reliefs on the hub insert, the invention inverts the approach by forming simple reliefs directly on the rim itself during the casting process. The rim is cast with integrated attachment features that provide the necessary torsional resistance, thereby eliminating the need for complex insert manufacturing while achieving the same junction strength.
Solution Approach 2:
The attachment reliefs are formed preliminarily during the rim casting operation itself, rather than requiring subsequent complex machining or modification of the hub insert. This preliminary formation of attachment features on the rim simplifies the overall manufacturing process while ensuring adequate torsional shear resistance at the hub-rim junction.
4Strength
If a metallic hub with large diameter is used to support the rim, then structural support is improved, but the weight of the obtained wheel increases
Solution Approach 1:
The invention uses a composite structure where a polymer rim is cast around a metallic hub insert, combining the advantages of both materials. The metallic insert provides the necessary structural support and strength, while the polymer rim reduces overall weight compared to a fully metallic construction. The composite design optimizes the support capability-to-weight ratio by placing each material where it is most effective.
Solution Approach 2:
Instead of using a large-diameter metallic hub throughout, the invention applies the metallic material only locally where structural support is actually needed at the center, while the lighter polymer material forms the outer rim. This local quality approach provides adequate structural support with minimal metallic content, thereby reducing overall wheel weight while maintaining necessary strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method preserves polymer chain integrity, enhances mechanical resistance and longevity, reduces material and energy consumption, and allows for versatile rim production with different heights, while maintaining simplicity and mechanical effectiveness in tooling, and achieving a lightweight wheel with adapted mechanical properties.
Implementation Method 1
casting a liquid to be polymerized in a first mold and polymerizing said liquid in said first mold so as to be solidified into a tubular preform
Data Source
AI summary
A method for manufacturing a wheel including a step (a) during which a liquid to be polymerised is cast into a first mould so as to solidify same into a tubular preform, with main axis, the first mould including modelling cores in order to form recesses, of the rib type, in the radial thickness of the tubular preform; followed by a cutting step (b), during which the tubular preform is cut perpendicular to the main axis thereof, and secant to the recesses, so as to obtain a tubular preform section forming a rim; followed by an overmoulding step (d), during which said rim is placed in a second mould, concentrically with a central supporting member, such as a bushing or a shaft, and a polymer filling material is injected so as to create an intermediate disc that provides the attachment of the rim to the central supporting member.